1. Field of the Invention
The present invention relates to a novel composition containing a liquid crystal phase, and in particular, to a lipid composition comprising a mixture of compounds belonging to the ceramide family and a medium suited for cosmetic or pharmaceutical use.
The lipid composition according to the invention may comprise a racemic 2-acetaminoalkane-1,3-diol, i.e., N-acetylsphinganine, or an optically active form thereof; a racemic 2-acylaminoalkane-1,3-diol or an optically active form thereof; and cholesterol, and optionally a cholesterol ester, e.g., cholesteryl hydroxystearate; iso-stearic acid; and/or other higher fatty acids.
The composition may further comprise a triglyceride, a phospholipid or other cosmetically or pharmaceutically acceptable vehicles or excipients. Such a composition may especially be appropriate for use as a cosmetic product, an externally applicable skin preserver, a bath additive, a hair-care product, or the like.
The composition described above is capable of retaining moisture on the subject to which it is applied. When it is applied on the skin, it renders skin humid and fair, and reactivates skin cells. The composition thus protects the skin and provides a suitable cosmetic, dermatological or bath-additive product. When applied to the scalp or hair, subsequent hair-washing does not cause a loss of water-soluble proteins or amino acids from hair so that it is protected from drying-out.
To render the skin moist and smooth, the water content retained in the stratum corneum (horny layer) of the skin plays an important role. Water seems to be retained in this stratum corneum by free amino acids, organic acids, urea, inorganic ions or the like, contained therein. Such substances are actually used alone or in combination for preparing a dermatological cosmetic product or medicine for external application, in order to prevent or cure rough skin.
2. Description of the Prior Art
It has been found only recently that intercellular lipids contained in the stratum corneum have a high water-retaining capacity and usually contain about 30% water. These lipids control the evaporation of corporal water and prevent external stimulants from penetrating, to thereby preserve the tenderness and smoothness of the skin.
Among the intercellular lipid components, a ceramide in particular, but also a cholesterol ester, are known to improve rough skin when applied thereto. Especially, the ceramide serves as an efficient barrier to water migration.
The intercellular lipids consist mainly of ceramides, cholesteryl sodium sulphate, palmitic acid and cholesterol. In view of the above, a composition containing these same components, in which the ceramide corresponds to a racemate having the formula (II), was prepared and described in Japanese Unexamined Patent Application No. Hei 4-327563.
Conversely, it was found that the level of ceramide content in a patient suffering from rough or dry skin, or atopic dermatitis is considerably low, as compared with the skin of a healthy person.
Ceramides were also isolated and identified by G. Hussler et al. from lipids contained in human hair (Int. J. Cosmet. Sci., 17, 197, 1995). These ceramides have a high capacity for retaining water. A racemic ceramide was then synthesized and incorporated into a lipid composition for hair-washing. It was proposed that the lipid composition reduces the loss of proteins and amino acids from hair when it is washed to protect and prevent the hair from drying-out (European Patent 0 278 505).
It was also reported by M. Philippe et al. that a composition containing a synthesized racemic ceramide reduces the water loss of hair (Int. J. Cosmet. Sci., 17, 133, 1995).
Under these circumstances, research is currently being carried out into the application of ceramide-containing, intercellular lipid-type substances to rough skin, in view of improving the state of the skin.
Ceramides are scarcely soluble in water or any organic solvent. To provide ceramides in the skin, it is thus necessary to first prepare a lipid composition having a specific mixture ratio so as to form a lamellar liquid crystal structure, and to put this intact structure into a cosmetically or pharmaceutically usable form. The lamellar liquid crystal structure can be formed by adding a fatty acid or cholesterol to the ceramide. The ceramides can be dissolved in a fatty acid, and then incorporated into the lamellar liquid crystal structure. For the above purpose, a surfactant is usually added to promote penetration of the lamellar liquid crystal structure into the skin, but crystals other than the ceramides should not be added thereto. Moreover, a specific sort of surfactant must be selected in order to promote the penetration of intercellular lipids into the stratum corneum and also to promote the formation of a lamellar liquid crystal. The intercellular lipids consist mainly of a ceramide, cholesterol, a fatty acid such as palmitic acid and cholesterol sulphate. A mixture of these components usually forms a lamellar liquid crystal structure. This structure can also be formed in the absence of the fatty acid or cholesterol sulphate. However, according to the report by P. W. Wertz et al., the ceramide alone, or together with cholesterol, does not form a homogeneous lamellar liquid crystal structure (J. Invest. Dermatol., 87, 582, 1986).
On the other hand, a hair-protecting composition has been proposed consisting of a ceramide or glucoceramide, a cholesterol ester and a cosmetically acceptable vehicle (Japanese Unexamined Patent Application No. Sho 63-270617). The ceramide or the glucoceramide, e.g., cerebroside, used in this composition is extracted from a material of animal origin such as pig skin, bovine brain and red corpuscles (haematid), or from a plant. Among these possibilities, bovine brain extract is considered to be the most appropriate product. However, since the eruption of bovine spongiform encephalitis (mad cow disease), this product may no longer be used.
A hair-protecting composition has also been proposed containing either a ceramide or glycoceramide and at least one kind of cholesterol ester (Japanese Patent No. 2,510,235).
In another study, a lipid component was selected from the group consisting of a ceramide, a pseudoceramide, a polyester consisting of a polyol and a fatty acid, a phospholipid, a galactosyldiacylglycerol, a sphingoglycolipid, a derivative of succinic acid and a mixture thereof and incorporated into a lipid lamella, in order to cure xeroderma (Japanese Unexamined Patent Application No. Hei 6-157283).
Furthermore, a composition has been provided for use as a bath additive containing a ceramide and a compound having a pseudo-ceramide structure (Japanese Unexamined Patent Application No. Hei 8-34726).
Still further, a mixture was prepared containing a complex product or composition having a liquid crystal phase, an amphoteric and/or semi-polar surfactant, a higher fatty acid and water. Use of the mixture allows cosmetic make-up to hold properly and longer, and to more efficiently resist the deteriorating effect of water and cutaneous fat (Japanese Unexamined Patent Application No. Hei 8-217633).